EDAC: Fix sysfs dimm_label store operation

EDAC: Fix sysfs dimm_label store operation

Sysfs "dimm_label" and "chX_dimm_label" nodes have the following issues
in their store operation:

 1) A newline-terminated input string causes redundant newlines:

  # echo "test" > /sys/bus/mc0/devices/dimm0/dimm_label
  # cat  /sys/bus/mc0/devices/dimm0/dimm_label
  test

  #  od -bc /sys/bus/mc0/devices/dimm0/dimm_label
  0000000 164 145 163 164 012 012
            t   e   s   t  \n  \n
  0000006

 2) The original label string (31 characters) cannot be stored due to
    an improper size check:

  # echo "CPU_SrcID#0_Ha#0_Chan#0_DIMM#0" > /sys/bus/mc0/devices/dimm0/dimm_label
  # cat /sys/bus/mc0/devices/dimm0/dimm_label

  # od -bc /sys/bus/mc0/devices/dimm0/dimm_label
   0000000 012 012
            \n  \n
   0000002

 3) An input string longer than the buffer size results a wrong label
    info as it allows a retry with the remaining string:

  # echo "CPU_SrcID#0_Ha#0_Chan#0_DIMM#0_TEST" > /sys/bus/mc0/devices/dimm0/dimm_label
  # cat  /sys/bus/mc0/devices/dimm0/dimm_label
  _TEST

Fix these issues by making the following changes:
 1) Replace a newline character at the end by setting a null. It also
    assures that the string is null-terminated in the label buffer.
 2) Check the label buffer size with 'sizeof(dimm->label)'.
 3) Fail a request if its string exceeds the label buffer size.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Acked-by: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: Robert Elliott <elliott@hpe.com>
Link: http://lkml.kernel.org/r/1443121564.25474.160.camel@hpe.com
Signed-off-by: Borislav Petkov <bp@suse.de>